Is 'metacity' running?
Try: 'ps algx | grep metacity'. If nothing, then metacity is not running.
Try starting it from one of your (misplaced) terminal windows:
'metacity&' and see what happens.
Is 'gnome-panel' running? If not, do similar as above.
Also, there has been a problem with some of the latest
'xorg-x11-xinit' packages. Which one are you running? If 1.0.2-7,
rename /etc/X11/xinit/xinitrc.d/localuser.sh to something harmless.